Exterior Stain on wood

How to Stain Outdoor Wood for Durability

by Lawrence Winterburn

Exterior Stain on Wood

Our clients are always shocked when we tell them that they can stain a deck and make it last a few years before it needs maintenance. Many people assume that our work is made of composite wood, rather than milled timber. Truth is, all our work is wood, mostly red and white cedar and many of the decks and pergolas you see on our site were photographed years after the first stain application.

The following is our HOW TO guide to applying exterior stain to cedar decks, timber pergolas, fences and any other garden structures made of wood. We are not satisfied with telling you how to apply the stain, but also why exterior stain fails.

Choosing a good Exterior Stain:

Canada has banned high VOC exterior stain. I really don’t care why, but high VOC coatings tend to last longer in the elements. High VOC coatings can still be used for concrete finishes and many paints, but these formulations are now banned for deck stain across the country. The current Canadian made offerings that we have tried since the ban came into effect a couple of years ago don’t last as well as the old alkyd stains we used to get 5 years of durability from.
So, if you live in Canada, my advice is, and it pains me to say it–Buy American Made High VOC coatings like Flood or Superdeck. Many are sold here, and none are made here, and the US is still producing it. It is the most similar formulation to the old oil based Benjamin Moore that used to work so well.

In general, paint lasts longer than stain, however it deteriorates and marks on horizontal surfaces. The solid stain lasts longer than semi-transparent in general terms. There are many different companies which make numerous products with benefits and drawbacks to all of them. Generally, a good choice of stain will contain plenty of pigment for UV protection, a mildewcide, and fungicide and be oil based.

Often price has little to do with the quality of stain–though, if you want to spring for an epoxy marine finish at a couple of hundred per gallon, you might notice a difference in durability. Generally, good stain ranges between $35 and 70$/gallon in Canada, 25% less in the US.

Our Solutions to Peeling Stain:

Plants absorb and store moisture and nutrients in the root structure then draw them up the stem as required. Trees are simply just a large plant which means that lumber is that stem sliced up. Think of a redwood tree 150’ in height drawing moisture from the roots and feeding it to the branches. The larger the species, the longer the cells, and, the greater the suction created of moisture through the end grain. This means the wood has a natural tendency to draw moisture into the end grains and expand as they do so.

Solution 1: Seal the end grains too.

As a plant is dehydrated, it shrinks. Trees, being large plants behave in exactly the same way. In fact, if a tree is left whole after cutting, they will tend to develop cracks to the center, larger in the outer grain, smaller in the center grain. If you have ever noticed a fence post, which is cracking all 4 sides, that indicates that the core of the tree is in the center of the timber. That core of the tree’s closest route for the crack is to each flat surface of the post.

Solution 2: Seal all 4 sides as well as the ends to stabilize moisture content.

Solution 3: If you cut a timber seal the end again during assembly.

During the planing process (smoothing of wood), superheated sap and sawdust is forced into the surface of the wood. This “mill glaze” is similar to glass and stain will not penetrate it. You can see the mill glaze if you look at the surface of the wood from an angle and the surface is shiny or glass like.

Solution 4: Before applying stain, sand all surfaces with 80 grit sandpaper to open up the cells of the wood to accept the stain.

Solution 5: Rollers will lay stain on fast, however, it won’t get the stain into the pores. Apply stain with a roller but give it the once over with a brush. Brush everything in 2 directions for maximum penetration. If the stain is a thick consistency, dilute the stain you use for the first coat a little, to help it enter the pores more readily.

Back Brush with a paint brush after applying the stain.

Solution 6: Stack your lumber with 1 or 2” spacers between layers, boards 1” away from each other. Plug a couple of fans in, and open the garage door a crack. Dry the lumber for a couple of weeks before you sand it to remove the glaze.

Dry the lumber first — and keep it dry until the stain is applied.

Solution 7: Coatings tend to fade over time. Vertical surfaces will weather at different rates than horizontals. If you have decided to re-stain only part of your deck, you may find it is now 2 different colors. This is particularly true when it comes to semi-transparent coatings.

Consider staining the deck surface in a semi-transparent, and use a solid color on the verticals, (paint or stain). When it comes time to re-coat the horizontal surfaces, you won’t have to do the verticals as well.

Solution 8: All stains are made of chemicals and compounds that are mixed. They all require stirring prior to application. Direct sunlight can cause the materials in the stain to separate, which will cause poor results. Often humidity or moisture will cause the stain to contaminate. If it is too warm or too cold stains often will give poor results.

Apply your stain on a warm, dry, overcast day for best results.

Solution 9: Plants need moisture to live. At the time of harvesting trees have a high moisture content. During the production and finishing, the timbers lose some moisture, but only kiln drying will get most of the moisture out of the wood. Your typical lumber is about 18-22% moisture content. Kiln dried typically has about 5-8%. Before drying, that moisture resides in the pores of the wood, where you want the stain to be. That moisture, when it freezes, will expand and release the stain from the wood.

Dry the lumber first, or source kiln dried lumber for your project.

Q&A

How long should a stain job last?

If you follow the guide above, 2-3 years on horizontals due to wear from foot traffic and other factors. 4-7 years on verticals. If you just slap the stain on after the structure is built, you may get a year or two before it peels off.

In choosing stain color, are there any guidelines?

We like to borrow colors from the exterior of the house. Trim colours for rails, (to imitate a wainscoting), floor colors for the deck (often semi transparent to make it an extension of the floor in the house).

Can I use a spray gun or rig to apply the stain?

Sure, but just be careful you don’t spray your neighbor’s car, house, children…and run a brush over the whole board end to end twice to help penetration.